Remove ARCH_NAME ENV from UMD tests

[blozano-tt]

UMD tests require the whole repo is built 3x if we are to build with their test cases.

Need to fix that.

I suggested a fix here:

tenstorrent/tt-umd#51 (comment)

[blozano-tt]

I learned recently that we actually build UMD tests on the test VM.

So this is not a blocker.

Closing, because this is already tracked in UMD repo.